Simulation Techniques in CAD-CAM Processing by Milling

of Surfaces on NC Machine-Tools

GHIONEA IONUT1, GHIONEA ADRIAN

2

1Lecturer Eng. PhD., Machine Manufacturing Technology Department

2Professor Eng. PhD., Machine and Manufacturing Systems Department

University POLITEHNICA of Bucharest, Faculty of Engineering

and Management of Technologic Systems

Splaiul IndependenŃei 313, Bucharest, code 060092

ROMANIA

ionut76@hotmail.com adrianghionea@yahoo.com http://www.ghionea.ro

Abstract: - The paper presents theoretical and practical-applicative aspects on some methods for the NC

simulations using the CATIA v5 software, Machining module. An application is proposed for the milling procedure to process complex surfaces (plane and complex sculpture surfaces). Some practical optimization criteria are used, such as: correct choose of the machine-tool, type and durability of the cutting tools, paths and

division patterns of the stock left for machining, optimum cutting parameters (cutting speed and feed speed), efficient use of the machine-tool, reduction of the machining time, precision conditions etc. The paper contains

images and numerical data obtained from simulations allowing to draw conclusions regarding the possibilities to optimize the generation of complex surfaces whose generating and directing curves are not defined analytically.

Key-Words: - CAD-CAM, machining parameters, NC manufacturing simulation, optimization criteria, CATIA

1 Introduction To develop the processing steps for a mechanical part on a NC machine-tool involves generation of control data, stored in a predetermined sequence in a

specific ControlPanel equipment [7]. The main stages are: 3D representation of the

part, setting the technological operation sheet, choice of the working parameters, choosing the

strategy of division patterns of the stock left for machining, simulation processing, generation and checking the NC program.

These programs can be generated directly on the machine-tool, the operator writes the necessary

instructions using the available interface or by using a CAD-CAM program and a virtual model of the piece [4].

Defining the piece in a CAD environment is used as the entry data to generate the NC program with a

complex existing programming languages. Thus, the simulation is justified to optimize the process because CAM programs elaborate and list the NC

machine code. Each processing program for the part, compatible with the machine-tool, consists of a

sequence of sentences written in a logical sequence based on a specific syntax.

The machine-tool command is provided by the

numerical control equipment (NCE), designed

especially for the following types of machine-tools: lathes, milling, grinding, hobbing machines [8]. Their complexity is determined by the number of

numerically controlled axes and precision processing [11].

The machine-tools, by their kinematics structure, execute simple and precise movements (rotation R, translation T) in relation to the numerically

controlled axes [5], [8]. The correct assessment of these axes is imposed by standards and

recommendations. The axes of coordinates are assigned to couples

of translation (guideways) and/or rotation of the

machine [6]. The trajectories that define the generated surfaces result from the combination of

two, three or more simple movements, with determined speeds.

On the modern CNC equipments the user may

program, in addition to coordinates, other geometrical information regarding the compensation

of tools’ wear (lengths and diameters). Thus, it is possible to make various corrections

on: the dimensions, the wear of the cutting edge [2],

the amount of deformations, the level of tool’s vibrations, and of the vibrations appeared in the

fixture devices clamping the part on the machine-tool [1] etc.

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2 Initial Conditions In the current analysis it is used a machine-tool of vertical processing center (MCV) type, 5-axis (3

translations and 2 rotations) numerically controlled. The CAM processes on the machine-tool are

simulated in the CATIA v5 working environment, along with the cutting tools, toolholders, and necessary fixture devices.

The process parameters consist of the cutting regimes, the tools paths in the processing

movements etc. By simulation there were analyzed the generation

of the part’s surfaces based on different ways of

dividing the stock left for machining. Also, the processed surfaces’ roughness parameters Ra may be

geometrically evaluated. A simplified representation of the machine, its

axes and its mobile units are presented in Fig. 1. The X, Y and Z axes assure movements for feed

and/or positioning on the longitudinal (LS),

transversal (TS) and vertical (VS) directions, shown on figure. The TS slide is equipped with a tilting

rotary table having independent rotation motions on the A and C axes. The cutting tool T is fixed in the main shaft MS, part of the mobile assembly VS.

Fig. 1.

The sizes of the used stock are 120×120×35 mm,

made from a high alloyed steel material (HB=250), clamped with a special fixture device on the

machine-tool’s rotary table RT. The part is represented in Fig. 2 as a 3D model,

having a prismatic form and it is provided with

cavities and prominences. The part surfaces (S1-S9) can be processed by

simulation in the CATIA v5 CAM environment after an analysis in terms of shape, size and disposing of the machined surfaces.

Fig. 2.

Choosing of the machine-tool and of the milling head was determined mainly by the numerically

controlled axes number and positions, the stroke lengths, the diameter of the rotary table, the range of

the spindle speeds, of the feed speeds, of the quick motions, the dimensions of the working space etc. Also, it was taken into account the positioning

accuracy and repeatability of the machine, the collisions avoiding and the stability of the cutting

process [10]. It is recommended that, during the processing, the tool rotation axis at any point of the machined surface to be perpendicular to the tangent

to the generated trajectory. The chosen machine-tool has the following

technical characteristics: rectilinear movements, max., on axes X = 800 mm, Y = 600 mm, Z = 500 mm, circular movements, max. A = -1100 ... 1100

and C = 3600, spindle speed max.: 15000 rpm, the power of the main electric engine: Pn = 12 kW, the

torque Mc = 53 Nm, the power of the electric engines for the feed/positioning movements: X-axis

and Y-axis: 4 kW, Z-axis: 5.5 kW, machining feedrate max.: 6000 mm/min and rapid feedrate: 30000 mm/min, tool magazine: number of tools: 24,

tool changing time: 2 s, chip-to-chip time: 5 s, the toolholder cone type: HSK; NC system: Sinumerik

840. Some of the features listed are inserted into the Numerical Control tab (Fig. 3) available for selection of the NC equipment in the CATIA

Machining module [4].

Fig. 3.

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In order to establish the technological system [3], there are defined the cutting tools and the necessary

fixture devices for the application of the machining processes. These data are inserted in the CATIA program during the simulation phases of each

processing operation for the technological process. The fixture devices and the toolholders are not

defined by default in the program, but they are taken into account by the user when choosing a surface of

the part that will not intersect the feed/positioning movement paths of the tool. Also, the simulation is possible to avoid collisions, especially in the case of

movements on A and C axes [5], [6]. The CATIA v5 program allows the user to define the cutting

tools, offering many options (corresponding to the technological process).

For the stock’s material there are selected tools

from specialized catalogs. For this application, the cutting tools are provided with ISO P20 inserts

(Coromant Catalogue steel milling grades) [12]. The user can determine the main features/code for each tool: diameter and length of the active part, total

length, diameter and shape of the toolholder, number of teeth, the tool type for the corresponding

surface shape and for the applied technological process etc. For the current analysis, in the paper are presented some data regarding the characteristics of

each cutting tool: material and form of plates, cutting edges geometry, constructive angles of the

tool’s edge, recommendations of use etc.

Fig. 4

For example, Fig. 4 shows some data inserted in the appropriate fields available in the CATIA v5 program referring to the tool CoroMill 245.

3 Stages and Results of the CAM

Simulation The part’s shape analysis and the number of processing surfaces, noted on the part 3D model

(Fig. 2), indicate, as necessary, several technological processes: rough face milling (S4), rough contour

profile milling (S1, S2, S3), semi finish complex

milling (S1, S2, S3, S5, S6), finish complex milling of the surfaces previously processed.

3.1. Stages, processing and tool paths In this paragraph are presented the milling processes of the surfaces whose generating and directing

curves are not defined analytically. Figure 5 shows successively the following processing sequence:

face milling 120×120 mm, depth 2 mm, in one pass (5, a.), external contour profile milling 120×120 mm, depth 20 mm, in four passes on the depth of the

stock left for machining (5, b.), external contour profile and cavities semi finish milling, strategy

Spiral (5, c.). For the finishing milling process, it is used the Zig-Zag strategy [4], [13], in 5 axes, on two

directions (5, d. and 5, e.). The first direction is on the X axis and the second on the Y axis, with repositioning between two consecutive paths. Some

figures have a small detail image for a better understanding of the generated tool trajectory.

Fig. 5, a.

Fig. 5, b.

Fig. 5, c.

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Fig. 5, d.

Fig. 5, e.

Table 1. Data of the simulation process

No.

Name of the

technological

process

Cutting tool [12] Process parameters*

Duration

tm tt

1

Rough face milling

(fig. 5, a)

Face mill with 5 teeth, CoroMill 245/GC 1025,

Кr=450

D3 = 62.5, Dc = 50, ap = 1, ae = 25,

hex = 0.15, fz = 0.21, vc = 170, nc = 1041, vf = 1100, Pc = 1.5,

Mc = 14, Q = 27

0.7

5

0.8

8

2

External contour profile rough milling (fig. 5, b)

Profile milling cutter with 5 teeth, CoroMill 300/1030

D3 = 42, Dc = 32, ap = 5, ae = 10, hex = 0.12, fz = 0.12, vc = 120,

nc = 909, vf = 630, Pc = 2.1, Mc = 14, Q = 32

2.9

8

3.1

3

External contour profile and

cavities semi finish milling (fig. 5, c)

Ball nose end mill with 2 teeth, CoroMill 216/P, GC 2040, Main inserts

E-M

D3 = 10, rƹ = 0.3, l2 = 160, ap = 3, ae = 4, hex = 0.05, fz = 0.05, vc = 180, nc = 6250, vf = 625, Pc = 0.5,

Mc = 0.8, Q = 8

12.4

5

12.5

4

4

External contour

profile and cavities finish

milling, X axis, repositioning on Y axis (fig. 5, d)

Ball nose end mill with 2 teeth, CoroMill 216/P,

GC 2040, Main inserts E-M

Variant I: D3 = 10, ap = 0.2, ae = 2, hex = 0.015, fz = 0.015, vc = 180,

nc = 20460, vf = 614, Pc = 0.4 20.8

7

21.3

5

Variant II: D3 = 10, ap = 0.2, ae = 2, hex = 0.015, fz = 0.015, vc = 125, nc = 14000, vf = 420, Pc = 0.3

21.2

21.6

7

5

External contour

profile and cavities finish milling, Y axis,

repositioning on X axis (fig. 5, e)

Ball nose end mill with 2 teeth, CoroMill 216/P, GC 2040, Main inserts

E-M

Variant I: D3 = 10, ap = 0.2, ae = 2, hex = 0.015, fz = 0.015, vc = 180, nc = 20460, vf = 614, Pc = 0.4 2

1.4

6

22.1

2

Variant II: D3 = 10, ap = 0.2, ae = 2, hex = 0.015, fz = 0.015, vc = 125,

nc = 14000, vf = 420, Pc = 0.3 21.8

3

22.3

7

* D3 (mm) – tool diameter, Dc (mm) – cutting diameter, l2 (mm) – tool length, ap (mm) – cutting depth, ae (mm) – working engagement, hex (mm) - chip thickness, fz (mm) – feed per cutting edge (mm), vc (m/min) - cutting speed, nc (rot/min) -

spindle speed, vf (mm/min) - feed speed, Pc (kW) - cutting power for removal of chips, Mc (Nm) - cutting torque, Q

(cm3/min) – metal removal rate, tm (min) – machining time, tt (min) – total time.

Position of the tool axis from the machined

surface is obtained on the machine-tool by orienting the part with movements on the A axis. The

simulation spreadsheet data are shown in Table 1

with reference to: tools, trajectories, cutting and

generation parameters and, also, the required processing time (tm – machining time and tt – total

time).

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3.2. Results Applying the simulation methods resulted the parameters given in Table 1. Inserting these

calculated parameters in a practical case in a CAM program on the real milling machine-tool having nc max = 15000 rpm is not possible to comply in

variant I for the processings 4 and 5 (finish millings in table 1) in which the calculated spindle speed (nc

= 20460 rpm) exceeds this maximum value. Thus, for the finish millings the user must choose a lower spindle speed value, 14000 rpm, and the simulation

process parameters vc, vf and Pc are recalculated (variant II).

For the optimization by simulation in the CAM environment provided by CATIA there are proposed

the following criteria: tools trajectories and the number of passes (division pattern of the stock left for machining), precision and surface quality

conditions, processing duration, behavior of the machine-tool in working conditions (power and

cutting torque, a low number of sense reversals of feeding motions and positioning), behavior of cutting tool (tool body and tool holder rigidity,

vibration level [8], maintaining durability) by a uniform using of the cutting edge.

In the simulation process there were applied different trajectories to obtain the generating and directing curves. The generation of the analyzed

surfaces require precise working movements defined according to the strategies adopted for tools

paths. Also, there are auxiliary movements: for positioning, for rapid approach and retract, for wear compensation of the tool cutting edge, for changing

the tool.

Fig. 6

CATIA allows the user to set up certain options in relation to these criteria: the tool path is chosen of

the following variants: One-way next, One-way

same, Zig-Zag, Spiral, Contour only, Concentric

and Helical. Also, it is important the milling type: down milling or up milling. The process parameters

were choosen, calculated and inserted in the fields of the dialog window (Fig. 6). To simulate the milling of the external contour profile and of the

cavities it was used a Ball nose end mill [12], Fig. 7, with two circular plates, the tool diameter is Ø10.

Fig. 7

Figures 8 show the processing steps of the

external contour surfaces and cavities: in Fig. 8, a. the face mill makes a semi finish milling. Fig. 8, b.

and Fig. 8, c. present the finish milling on the X axis direction, respectively, the finish milling on the Y axis direction. Fig. 8, d. is a detail with the surface

inside the circular cavity after both finishing processings.

The tools marks may be observed on both directions. Figures 8 show the tool movement according to the processing strategies (Spiral for

rough milling and Zig-zag for finish millings), and also the tool slope for the finish millings. For these

two successive processings there were used the 5-axis machine-tool capabilities.

Changing the tools trajectories, the cutting parameters, choosing different tools etc. aimed at optimizing by simulating the processings. Based on

the analysis results of the machined surfaces, the user must consider mainly the variants with the

lowest machining time. Thus, it is possible to process more parts in the

appropriate time prescribed for tool durability which

gives an increase of operation productivity. Also, the user may choose the variants with a higher

machining time, where the cutting tool is in contact longer with the cutting layer, resulting in a lower roughness, but, in the same time, the tool is subject

to an intense wear process.

Fig. 8, a.

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Fig. 8, b.

Fig. 8, c.

Fig. 8, d.

3.3. Generation of the part program

After rough, semi finish and finish milling processes by simulation applied on the analyzed part, the

CATIA software automatically generate the NC code.

Fig. 9

Figure 9 shows a fragment of the generated code,

the lines contain programming data from the processing of the external contour profile and

cavities finish milling. Five-axis milling assisted by CATIA v5 provides advanced methods for effective and optimized machining and surface finish.

4 Conclusion Learning the CAM simulation methodology is an important step necessary to the representation of

virtual machine-tools (structural configuration, working space, collision avoidance etc.) and to

further simulations on this virtual machine. The items which require further development are: tool path generation, control of simultaneous cutting,

selection of proper machining method, tool posture control, post processing.

The ultimate goal of CAM software is to generate the NC program directly from CAD data. Attempts are also being made to machine sculptured

surfaces directly from CAD data by introducing a concept of digital copy milling.

References: [1] Altintas, Y., Lee, P., Mechanics and dynamics of ball

end milling. Journal Manufacturing Science and

Engineering Transactions of the ASME, 120, 1998,

684-692.

[2] Astakov, V.P., Tribology of metal cutting, Elsevier,

2006.

[3] Brăgaru, A., Picoş, C., Ivan, N., Optimizarea

proceselor şi echipamentelor tehnologice. Editura Didactică şi Pedagogică, 1996, Bucureşti.

[4] Ghionea, I., CATIA v5. AplicaŃii în inginerie

mecanică. Ed. BREN, Bucureşti, 2009, 256 pag.

[5] Ghionea, A., Constantin G., Popa, C. L., Kinematic

structures and machining possibilities of some CNC machine tools. Buletin StiinŃific, Serie C, Volumul

XXIII, North University of Baia Mare, 2010,pp.45-52.

[6] Kief, B. H., NC/CNC Handbuch. Carl Hanser Verlag

Wien, ISBN 3-446-21756-8, 2001.

[7] Lazoglu, I., Sculpture surface machining: a

generalized model of ball-end milling force system. International Journal Machine Tools & Manufacture,

43, 2003, pp. 453-462.

[8] Lopez de Lacalle, N.L, Lamikiz, A., Machine tools

for high performance machining. Springer-Verlag

London Ltd, 2009.

[9] Mariwaki, T., Multifunctional machine tool. CIRP

Annals-Manufacturing Technology, 2008, 736-749.

[10] Ozturk, E., Taner, T. L., Budak, E., Investigation of

lead and tilt angle effects in 5-axis ball-end milling

processes. International Journal of Machine Tools&

Manufacture, 49, 2009, 1053-1062.

[11] Sun Y., Dongming Guo F.R., Jia, Z., Estimation and experimental validation of cutting forces in ball-end

milling of sculptured surfaces. International Journal

of Machine Tools & Manufacture, 49, 2009, pp. 1238-

1244.

[12] ***, Cutting tools from Sandvik Coromant. Main

catalogue. Turning. Milling. Drilling. Boring.

Toolholding, C-2900: 6 ENG/01. Printed in Sweden,

www.coromant.sandvik.com, 2012.

[13] ***, CATIA V5R21, – Official documentation.

Dassault Systemes, 2012.

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ISBN: 978-1-61804-193-7 140